There exists a need for the separation of the individual fatty acids or their esters from their mixtures, naturally occurring or formed from naturally occurring sources such as fats and oils. Separation of waxes and similar crystalline fractions from mineral oils is also such a desirable separation. In addition, this process lends itself to the separation of crystallizable components of solutions of organic compounds from mutual solvents. The organic compounds are crystallizable and are separated by the characteristic crystal growth of the component of the mixture from the solvent mother liquor.
In the past, such separation has been achieved by the indirect cooling, as by heat exchangers, of the liquids containing the dissolved components to be separated. However, the indirect cooling procedures result in adherence of the crystallized components to the surfaces of the indirect cooling means, the heat exchanger elements. This gives rise to mechanical separating problems including the removal of the crystals from the cooling elements to which they adhere. Such separation usually is accomplished by mechanical scraping elements.
Further since indirect cooling is limited in cooling rate by the cooling apparatus and this limited cooling rate becomes compounded by the crystals adhering to the cooling surfaces, the types of crystals found on the cooled surfaces are of insufficient purity for other than gross separation procedures.
It has been proposed to cool the mixtures by direct cooling by the evaporation of refrigerant in the mixture by BOSMAN et al; U.S. Pat. No. 3,554,896. Evaporation of the refrigerant as taught therein results in a slow lowering of the temperature of the mixture. The slow rate required by this prior art teaching, 1.5.degree. F./min, first forms crystals of the higher melting point components which are then gradually surrounded by the growth thereon of components of gradually lower melting points. As a result of the accretion of the lower melting components on the initial high melting crystals, crystal growth continues until the final crystals are of proper size for separation. However, the accreted material of lower melting point reduces the purity of the separated crystals.